You could try something with overpay. Like
Bomb(Action) -- $0P
+1 Action
Trash a card from your hand, then trash this card.
---------------
When you buy this, you may put your deck into your discard pile.
When you buy this, you may overpay for it. For each $2 you overpaid, search your discard pile for a card and trash it. Then, trash this card.
I think in this form, it would be pretty OP, because it lets you selectively trash. But, just having the Doctor overbuy would be too weak.
Maybe it would be slightly less powerful without the putting the deck into the discard phrase, but you'd just end up waiting for it, and I personally dislike waiting for shuffles. But something could be done with a one-off, on-buy trash.
I think it fits the theme of a bomb well. It costs potion because, well, you use chemicals to make bombs. More of a late game, get rid of exactly the 3 cards you need to for the cost of Possession.
And hey, if you ever find a way to get it into your deck(Swindle a Transmute?), it still at least does what the original did. Also, I think the way I worded it, you could still buy it normally at $0P and have it go into your deck.